Microscopic Mechanism of the Helix-to-Layer Transformation in Elemental Group VI Solids

TL;DR

This study uncovers the atomic-scale mechanism behind the transformation of bulk selenium and tellurium into novel 2D layers, revealing low-energy pathways and stable allotropes through ab initio calculations.

Contribution

It introduces a detailed multi-step reaction pathway involving dislocation motion for the helix-to-layer transformation in Group VI solids, identifying new stable 2D allotropes.

Findings

Stable ta- and \u03b4 -2D allotropes identified

Low activation barriers (<0.3 eV) for transformation

All 1D and 2D chalcogen structures are semiconducting

Abstract

We study the conversion of bulk Se and Te, consisting of intertwined a helices, to structurally very dissimilar, atomically thin two-dimensional (2D) layers of these elements. Our ab initio calculations reveal that previously unknown and unusually stable \delta - and \eta-2D allotropes may form in an intriguing multi-step process that involves a concerted motion of many atoms at dislocation defects. We identify such a complex reaction path involving zipper-like motion of such dislocations that initiate structural changes. With low activation barriers <0.3 eV along the optimum path, the conversion process may occur at moderate temperatures. We find all one-dimensional (1D) and 2D chalcogen structures to be semiconducting.